1. Field of the Invention
This invention is directed to a novel concept wherein polarity gradients are induced by a distillation process whereby enhanced multi-solvent extraction of petroleum residua and heavy oils produces low CCR maltenic fractions and high CCR asphaltenic fractions. This invention is further directed to the use of a distillation separatory process to establish a concentration gradient between a high polarity and a low polarity solvent within an extraction column, said polarity gradient acting to enhance distinct partitioning of CCR (Conradson Carbon Residue), metals, nitrogen and sulfur during the extractive separation of the asphaltenic and maltenic fractions of petroleum residua or other heavy oil.
2. Description of the Prior Art
Solvent extraction is a well known process in the refining of petroleum, being established as early as 1911. Solvent extraction is used in the petroleum refining industry for a multitude of purposes such as upgrading charge stocks for catalytic cracking operations.
Solvent deasphalting is also a well-known operation in refineries today. The primary objective of deasphalting is to separate a petroleum stream into a relatively high quality fraction ("deasphalted oil" or "maltenes") and a lower quality fraction ("asphalt" or "asphaltenes"). The asphaltenes are generally higher in aromaticity, Conradson Carbon Residue (CCR), molecular weight, and heteroatom (S N, Ni, V, Fe, etc.) content. Solvent deasphalting may also be thought of as a simple form of compositional delineation. Many methods are currently available for separating hydrocarbons into more distinct compositional groups. An example of such a method is gradient elution chromatography (GEC), where a sequence of increasingly polar solvents are used to isolate various hydrocarbon types. In contrast to these prior art methods this invention utilizes a process of distillation to isolate various hydrocarbon fractions.
As light crude stocks become less available, refineries are turning to heavier crude stocks for gasoline and distillate production. However, these heavier crudes result in increased quantities of high CCR, hard to process vacuum residua. This extraction process will allow the vacuum residua to be sharply cut to give maximum yield of a low CCR maltenic fraction suitable for catalytic cracking. The high CCR material will be concentrated into an asphaltenic cut which can then be coked or hydroprocessed and catalytically cracked. In the case of a resid HDT/FCC process, this will decrease the volume charged to the hydrotreater and subsequently reduce hydrogen consumption. Further, integration of Polarity Gradient Extraction into an existing refinery will permit processing of varied quality crudes. This process, due to its infinitely variable polarity gradient, can cut a stream to any yield or quality specification as required for downstream processing. Thus, with proper selection of solvents it is possible to partition the heteroatoms and CCR of a hydrocarbonaceous material in a manner analogous to disproportionation.